Currently, 3GPP has proposed a networking model which is different from a conventional networking model. In the networking model, a Base Station Controller (BSC) or a Radio Network Controller (RNC) may be connected to multiple servers. These servers may form an MSC Pool. The advantages of the networking model including the MSC Pool are as follows: within the MSC Pool, load sharing may be implemented among these servers; the interface signaling volume between the servers and the Home Location Register (HLR) may be reduced; within the MSC Pool, the interface information volume between the servers may be reduced so that call dropped rate is reduced; as for expansion, the planning of the core network and the radio access network may be done separately.
Regarding disaster recovery, the MSC Pool has an inherent disaster recovery function for a calling party. After a server serving a certain user is down, a new server in the MSC Pool will serve the user when the user initiates a calling service. However, for a called party, the user is unable to be called during a period of one periodic location update, and a new server in the MSC pool is able to serve the user only when the user initiates a location update after a period of one periodic location update. Specifically, if a server in the MSC Pool is down, the calling service for a user registered in the server that is down will not be affected; if the user does not initiate the calling service within a period of one periodic location update, the user cannot be called.
FIG. 1 shows a flow chart of signalings for a called party when a server is down in the prior art. MSC/Visitor Location Register (VLR) A and MSC/VLR B are two servers in an MSC Pool. A server in the MSC Pool is down (e.g., MSC/VLR A is down as shown in FIG. 1), a link from the HLR to the server is broken. When the HLR receives a Send Routing Information (SRI) message from a Gateway Switch Center (GMSC), since MSC/VLR A is down where the user is registered, the HLR is unable to send a Provide Roaming Number (PRN) message to MSC/VLR A, so that the HLR can not obtain a roaming number of the user from MSC/VLR A. Hence, the called party can not be called and connected within a period of one periodic location update.
If the user initiates a calling service or a location update during the period of one periodic location update, the called party can be successfully called after the user is registered in another server in the MSC Pool. If the user does not initiate any calling service or location update during the period of one periodic location update, the user can not be called as the called party successfully.
Therefore, it can be seen that the disaster recovery function for the called party in the conventional MSC Pool is not perfect. When a server is down, user information cannot be timely recovered, which makes it impossible for a user to be called as a called party successfully.